bio chapter 6

• Nucleic acid

  A biomolecule with DNA and RNA as types, with nucleotides as monomers
• Phosphodiester bond

  The bond between adjacent nucleotides in a nucleic acid polymer
• Nitrogenous bases

  • Purine (adenine, guanine), Pyrimidine (cytosine, uracil, thymine)
• Every organism has genetic material in the form of nucleic acids, with nucleotides as the monomer
• Genetic materials are found in all organisms, either DNA or RNA, with the ability to carry information and be copied
• Adenine binds with thymine, Guanine binds with cytosine


  Always forming a two-ring structure in DNA
• Purine and pyrimidine

  Purine has two rings, Pyrimidine has one ring
• Nucleotide components

  • Nitrogenous base (purine or pyrimidine), pentose sugar (deoxyribose or ribose), phosphate group
• RNA nucleotide contains ribose sugar and uracil instead of thymine
• Phosphodiester bond


  Forms a sugar-phosphate backbone in DNA
• Sugar-phosphate backbone


  Strong covalent bonds providing stability to the DNA structure
• Synthesis of DNA


  Reactions occur where monomers join together forming a phosphodiester bond
• Deoxyribose sugar doesn't have oxygen on the second carbon, just a hydrogen
• Linking of nucleotides occurs in the synthesis phase of DNA
• Complementary base pairing


  • A binds to T, G binds to C
  • Hydrogen bonds hold them together
  • Two hydrogen bonds between A and T, three hydrogen bonds between G and C
• Hydrogen bonds

  • Hold the two strands together and keep them from separating
  • Individual hydrogen bonds are weak but cumulatively strong
• Antiparallel means the DNA strands run in opposite directions, with one running from 5' to 3' and the other from 3' to 5'
• Hydrogen bonds only form between specific bases, leading to fewer mistakes in replication and transcription
• Hydrogen bonds can easily form without a chemical reaction, making it spontaneous and not requiring an enzyme
• Unwinding of a double helix

  The double helix structure is unwound to straighten it
• Helicase

  Breaks hydrogen bonds to separate the two DNA strands
• DNA polymerase


  Synthesizes a new strand of DNA and proofreads the DNA sequence
• Activated DNA nucleotides have two additional phosphate groups making them activated
• The number of chromatids always equals the number of DNA molecules in a cell
• DNA ligase

  Joins DNA fragments together and catalyzes the formation of phosphodiester bonds
• Enzymes needed for DNA replication

  • Helicase
  • DNA polymerase
  • DNA ligase
• Synthesis of new DNA strands


  Activated DNA nucleotides in the nucleus bind forming hydrogen bonds with bases on each exposed DNA strand
• DNA replication

  Semi-conservative process occurring in the S phase of interface where one DNA molecule becomes two DNA molecules
• DNA replication requires ATP
• During S phase, one chromatid becomes two sister chromatids
• No enzymes are required for the binding of activated DNA nucleotides with the complementary base pair
• Enzymes Helicase, DNA polymerase, and DNA ligase are all enzymes needed for DNA replication
• Leading strand


  • Synthesized continuously
• Lagging strand


  • Synthesized discontinuously as Okazaki fragments
• Each Okazaki fragment is formed by one individual DNA polymerase
• Two DNA molecules are formed, each containing one original strand and one newly synthesized strand, making it semi-conservative
• DNA replication


  1. As the DNA unwinds, another DNA polymerase is needed to start the process again

  2. DNA polymerase binds and continues the process as the DNA unwinds

  3. DNA polymerase is needed for the synthesis of the lagging strand in sections or as Okazaki fragments

  4. DNA ligase comes in to mend the Okazaki fragments and make it one long new strand